[Ffmpeg-devel] Re: [Ffmpeg-user] ffmpeg encoding, really slowvideo when recording with audio

[Luca Abeni]

Hello,

On Fri, 2006-02-03 at 12:10 +0100, Erik Slagter wrote:
> On Thu, 2006-02-02 at 20:54 +0000, Karl Lattimer wrote:
> >    I'm playing around with ffmpeg as it seems to be the only thing  
> > around that can record from line input and a composite video feed  
> > from a bt878 card. When I record video only I have no problem, the  
> > video plays back with exceptional quality and is absolutely perfect.  
> > However when I try and record audio from line-in also there seems to  
> > be a problem.
> > 
> > I am using the following command line to record with audio
> > 
> > ffmpeg -vd /dev/video0 -r 25 -b 2048 -ad /dev/dsp -s cif video.mpg
> 
> It's probably reading from /dev/dsp in blocking mode.
Well, ffmpeg opens the device in nonblocking mode, but if you are using
OSS drivers only few of them will honour the nonblocking behaviour.

An upgrade to recent alsa drivers (using OSS emulation, of course :)
solved the problem for me. If it is not enough, changing the "1.1" in
line 766 of ffmpeg.c ("if (vdelta < -1.1)") and following to something
like 2.0 or 3.0 should be needed.


Anyway, the good news is that the new v4l2 input format should not have
this problem...
A cvs update should be enough to get perfectly fluid video.
As a matter of fact, I am currently capturing video from an Osprey-100
card together with audio: the video is fluid (no dropped/duplicated
frames) and perfectly in sync with the audio :)

				Luca
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